1. Field of the Invention
The invention relates generally to the field of semiconductor device manufacturing and, more particularly, to methods for forming metal films by depositing and reducing metal oxide films comprising two different metals.
2. Description of the Related Art
In forming advanced semiconductor devices, metal films are used in a variety of contexts. For example, metal alloys such as nickel-iron alloys can be used in the magnetic heads of hard disk drives. Typically the Ni/Fe alloys are deposited by PVD methods. However, future device designs call for conformal deposition of the magnetic layers. Thus, more conformal vapor deposition processes, such as chemical vapor deposition (CVD) and atomic layer deposition (ALD) will be used in place of the physical methods.
In another application, metal films are used in the formation of silicides to be used as electrical contacts in integrated circuits. Typically silicides are formed by depositing a metal by a PVD method on top of silicon and annealing to induce a solid state reaction. Part of the silicon that is present in gate, source and drain structures can be converted into low-resistivity metal silicides. This is done to realize a conductive path with a low bulk resistivity on the one hand, and to ensure a good contact resistance on the other hand. In the past, TiSi2 was used for this process; then later CoSi2 was the silicide of choice for the most advanced devices. As both TiSi2 and CoSi2 consume a relatively large amount of silicon, there has been a switch to using NiSix to form these conductive paths. This silicide combines a low bulk resistivity with a relatively low amount of silicon consumption. In advanced devices, a second metal, such as Pt, is sometimes added to improve properties of the silicide, such as microstructure and thermal stability.
In these and other contexts, ALD would be beneficial for deposition in high aspect ratio structures. However, commercially viable methods for depositing many elemental metals have not been available. On the other hand, ALD processes for depositing metal oxides of these same metals may be known. Thus, one approach to forming metals has been to deposit metal oxides by ALD and subsequently reduce them to the desired elemental metal. However, there is a need for improved processes, such as processes that can be carried out at reduced temperatures.